Pandanus alkaloids in Stemonaceae: finding of a plausible biogenetic origin of Stemona alkaloids

Strategies for the synthesis of Stemona alkaloids: an update

Covering: 2009 to 2022The Stemona alkaloids, which are found in plant species from the family Stemonaceae, represent a tremendously large and structurally-diverse family of natural products. This review presents and discusses a selection of case studies, grouped by alkaloid class, that showcase the key strategies and overall progress that has been made in the synthesis of Stemona alkaloids and related compounds since 2009. Structural reassignments that have been reported over this period are also identified where necessary.

Alkaloids from Pandanus amaryllifolius: Isolation and Their Plausible Biosynthetic Formation

Pandanus amaryllifolius Roxb. (Pandanaceae) is used as a flavor and in folk medicine in Southeast Asia. The ethanolic crude extract of the aerial parts of P. amaryllifolius exhibited antioxidant, antibiofilm, and anti-inflammatory activities in previous studies. In the current investigation, the purification of the ethanolic extract yielded nine new compounds, including N-acetylnorpandamarilactonines A (1) and B (2); pandalizines A (3) and B (4); pandanmenyamine (5); pandamarilactones 2 (6) and 3 (7), and 5(E)-pandamarilactonine-32 (8); and pandalactonine (9). The isolated alkaloids, with either a γ-alkylidene-α,β-unsaturated-γ-lactone or γ-alkylidene-α,β-unsaturated-γ-lactam system, can be classified into five skeletons including norpandamarilactonine, indolizinone, pandanamine, pandamarilactone, and pandamarilactonine. A plausible biosynthetic route toward 1-5, 7, and 9 is proposed.

Suppression of IL-2 production and proliferation of CD4(+) T cells by tuberostemonine O

Tuberostemonine stereoisomers are natural alkaloids found in Stemona tuberosa, that are known to have anti-inflammatory and anti-infective properties. Tuberostemonine alkaloids inhibit inflammation by suppressing the expression of inflammatory mediators such as cyclooxygenase and nitric oxide synthase. However, the direct immunomodulatory properties of tuberostemonine alkaloids in T cells have not been elucidated so far. In this study, the activities in T cells of tuberostemonine N (TbN) and a novel alkaloid, tuberostemonine O (TbO), isolated from S. tuberosa, were investigated. Although TbN did not have a significant effect on cytokine production in splenic T cells, TbO selectively suppressed interleukin (IL)-2 production. Moreover, TbO, but not TbN, significantly inhibited IL-2 production by primary CD4(+) T cells and delayed the T-cell proliferation in a dose-dependent manner. Addition of excess recombinant IL-2 restored the decreased cell-division rates in TbO-treated CD4(+) T cells to control levels. Collectively, these findings suggest that the immunomodulatory effects of TbO occurred by the suppression of IL-2 expression and IL-2-induced T-cell proliferation, suggesting a potential beneficial role of tuberostemonine alkaloids for the control of chronic inflammatory and autoimmune diseases caused by hyperactivated T cells.

Pandalisines A and B, novel indolizidine alkaloids from the leaves of Pandanus utilis

Two novel alkaloids named pandalisines A (1) and B (2), constituting a new class of C8-substituted indolizidine moiety, were isolated from the leaves of Pandanus utilis. The structures of these new compounds were established by their mass and spectroscopic data. The absolute configuration was determined by the comparison of experimental CD and calculated ECD spectra. A plausible biosynthetic pathway for compounds 1 and 2 is advanced. The cytotoxic activities of the isolated alkaloids against A-549, Hep-G2, and MDA-MB-231 cancer cell lines were evaluated. The result showed that 1 and 2 are the first non-cytotoxic indolizidine alkaloids.

Recent Advances in the Synthesis of Stemona Alkaloids

Stemona alkaloids, featuring polycyclic structures and interesting bioactivities, constitute a distinct class from the Stemonaceae family. In this review, recent advances in the synthesis of these unique alkaloids are briefly discussed, highlighting the application of novel synthetic strategies to access the core structures, as well as creative solutions to the installation of multiple stereogenic centers. The literature reviewed in this article covers the publications from 2010 to November 2014, a period that witnessed the prosperity of the synthesis of Stemona alkaloids.

Studies on the asymmetric synthesis of pandamarilactonines: an unexpected syn-selective vinylogous Mannich reaction of N-tert-butanesulfinimines

Through an unanticipatedsyn-selective VMR, a highly enantioselective total synthesis of (−)-pandamarilactonine-A has been achieved.

Stemona Alkaloids: Biosynthesis, Classification, and Biogenetic Relationships

Stemona alkaloids form a unique class, which can be attributed to hemiterpenoid pyrrolidine- and monoterpenoid pyrrolidine-class alkaloids originated from L-ornithine and glutamic acid. By the end of 2013, approximately 183 Stemona alkaloids had been isolated from nature. The literature on Stemona alkaloids in the realms of chemical structure, synthesis, and bioactivities has been elegantly summarized and reviewed. We thus summarize in this review the biosynthesis, structural classification, and the intrinsic, biogenetic relationships of Stemona alkaloids. Based on the comprehensive consideration of biogenetic pathways and chemical features, the 183 Stemona alkaloids are classified into two classes (hemiterpenoid pyrrolidine- and monoterpenoid pyrrolidine) and fourteen types.

Alkaloids from the roots of Stichoneuron caudatum and their acetylcholinesterase inhibitory activities

Four new stichoneurine-type alkaloids, stichoneurines F and G (1-2) and sessilistemonamines E and F (3-4), have been isolated from the root extracts of Stichoneuron caudatum. The structures and relative configurations of these alkaloids have been determined by spectroscopic methods and molecular modeling experiments. Compounds 1-4 were tested for their acetylcholinesterase (AChE) inhibitory activities against human AChE. Compound 3 showed significant inhibitory activity with an IC50 value of 9.1±0.15 μM.

Metal-free [3 + 2 + 1]/[2 + 2 + 1] biscyclization: stereospecific construction with concomitant functionalization of indolizin-5(1H)-one

A metal-free [3 + 2 + 1]/[2 + 2 + 1] biscyclization strategy has been developed for the stereospecific construction with concomitant derivation of biologically significant indolizin-5(1H)-ones from simple and commercial starting materials. The transformations are notable because they can yield five new σ bonds and six stereocenters including a quaternary carbon center in a single operation.

Alkaloids from the Roots and Leaves of Stichoneuron halabalensis and their Acetylcholinesterase Inhibitory Activities

A study of the hitherto unreported Stichoneuron halabalensis Inthachub led to the characterization of the known compounds (+)-α-tocopherol and ( R)-(+)-goniothalamin; four known Stemona alkaloids, bisdehydoxystemoninine A (1), stemoninine (2), sessilistemonamine C (3) and sessilistemonamine A (4); and three new alkaloids, stichoneurine C (5), D (6) and E (7). The structures of these compounds were determined on the basis of their spectroscopic data. Alkaloid 7 showed significant inhibitory activity against electric eel acetylcholinesterase (AChE) (IC50 5.90±0.084 μM), while goniothalamin and compounds 1 and 2 showed significant inhibitory activities against human AChE (IC50 7.24±0.52, 5.52±0.13 and 3.74±0.09 μM, respectively).

A General, Enantioselective Synthesis of 1-Azabicyclo[m.n.0]alkane Ring Systems

In this Letter, we describe a novel approach for the general and enantioselective synthesis of a diverse array of small to large 1-azabicyclo[m.n.0]alkyl ring systems with an embedded olefin handle for further functionalization. The stereochemistry is established via a highly diastereoselective indium-mediated allylation of an Ellman sulfinimine in greater than 9:1 dr., which is readily separable by column chromatography to afford a single diastereomer. This methodology allows for the rapid preparation of 1-azabicyclo[m.n.0]alkane ring systems that are not readily accessible through any other chemistry in excellent overall yields and, for many systems, the only enantioselective preparation reported to date.

A versatile enantioselective synthesis of azabicyclic ring systems: a concise total synthesis of (+)-grandisine D and unnatural analogues

Closing in on azacines: We have developed a new six step approach for the rapid and enantioselective synthesis of indolizidine, pyrrolo[1,2-a]azepine, and pyrrolo[1,2-a]azocine azabicyclic systems and their respective lactam congeners, which are found in a host of natural products as well as pharmaceutical preparations. This protocol enables a concise enantioselective total synthesis of (+)-grandisine D in 16.4 % overall yield from commercial materials (see scheme).

Structural relationships of stemona alkaloids: assessment of species-specific accumulation trends for exploiting their biological activities

On the basis of a comparison of 42 Stemona samples, representing eight different species collected and cultivated in Thailand, species-specific accumulation trends of Stemona alkaloids were analyzed. An overview was achieved by comparative HPLC analyses of methanolic crude extracts of underground parts coupled with diode array or evaporative light scattering detectors. All major compounds were isolated and their structures elucidated by NMR and MS analyses. Protostemonine- and stichoneurine-type derivatives dominated, from which the latter characterize S. tuberosa and S. phyllantha accumulating species-specific isomers of tuberostemonine (3). The widespread S. curtisii and S. collinsiae clearly deviate by protostemonine-type derivatives dominated by stemofoline (10) and/or didehydrostemofoline (11). Further diversification within this structural type results from a mutual accumulation of derivatives with a pyrrolo- or pyridoazepine nucleus, leading to chemical variability in S. curtisii and S. aphylla.